There is an epidemic of chronic kidney disease (CKD) in El Salvador and Nicaragua. It has been a mysterious disease without enough study and data to determine its causes. Many of the victims have been sugar cane workers in the Central American countries.

A new study from researchers at Boston University suggests that working conditions in the cane fields, rather than exposure to agrochemicals, may be the main cause. A report from NPR describes some of the study's findings:

Now a new study from Boston University finds a clear connection between the disease and the work these men are doing.

"The decline in kidney function during the harvest and the differences [in kidney function] by job category and employment duration provide evidence that one or more risk factors of CKD (chronic kidney disease) are occupational," the report says.

In 2011 the study followed 500 sugar cane workers at one plantation, El Ingenio San Antonio in Nicaragua. The researchers found that the kidney function of field workers declined over the course of the six-month harvest. Sugar cane cutters and planters saw the sharpest drop.

"Finding that one or more risk factors are occupational is important," says Rebecca Laws, a doctoral student at the Boston University School of Public Health and lead author of the paper. "Before this, it was still sort of unknown whether the major risk factors were occupational or nonoccupational." ...

A growing suspicion that pesticides or herbicides are the culprit prompted the Salvadoran National Assembly to ban 53 agrichemicals late in 2013.

But this new study casts doubt on that theory. It found that field workers whose primary jobs were spraying for weeds and pests (and who thus had the most contact with agricultural chemicals) had the least decline in kidney function over the course of the harvest.

The researchers also found that dehydration among workers with the most physically demanding job — cutting cane — could contribute to the illness.

Cutters who drank more of a generic energy drink while on the job had less of a drop in kidney function than co-workers who drank less of the beverage.

Photographer Ed Kashi has been documenting the epidemic of kidney disease in Central America. In a recent interview he expressed optimism about possible prevention efforts based on the growing evidence of the occupational links for the disease:

Are there any simple interventions that can help reverse this epidemic?

We think introducing water, rest, and shade as prescribed by OSHA in the U.S. can do that in part, though concurrent with that intervention, we are absolutely looking at environmental contaminants. It's very promising.

Intervention also includes improving tools and work practices aside from water, rest, and shade to make the work day as productive but also as healthy and efficient (for the worker) as possible. What we've learned when it comes to manual labor -- and this is key -- is that efficiency and health are totally interdependent and related.